Combination manhole and fill

ABSTRACT

A manhole closure means for sealing a tank manhole aperture including an elongated strongback carrying a fill cover on its underside for covering a fill aperture in the closure means, such strongback being hinged to the manhole closure means at one side of the fill aperture for swinging movement over and onto the fill aperture in closed position. An elongated latch arm is hinged to the manhole closure means adjacent the fill aperture in a position opposite the strongback for swinging movement toward and away from the strongback. The latch arm has its hinged end bifurcated forming an opening in which the free end of the strong-back is received. Positioned on the underside of the latch arm adjacent the inner edge of the latch arm opening is a transversely disposed downwardly extending ridge. The strongback has at least one transverse recess formed in its top side adjacent its free end for receiving the latch arm ridge when the strongback free end is inserted in the latch arm opening, thereby firmly and securely locking the strongback and its fill cover over the fill aperture in closed position thereby effecting an over-center mechanism that prevents the fill cover from opening inadvertently due to impact or shock. The fill cover may also include a springwell and an annular gasket clamped between a cover disc and a gasket retainer, with the cover disc being threaded to the springwell. The fill cover may also include an integral springwell and a dovetail gasket carried in an undercut groove. The fill cover may also omit the springwell and secure resilient action by means of a resilient Belleville disc included in the fill cover structure. This resilient action is adequate for latching purposes, but not adequate for venting.

United States Patent 1191 De Frees 1451 July 10, 1973 Primary Examiner-Allen N. Knowles Assistant Examiizen-Michael Mar Attorney-Baldwin,Egan, Walling & Fetzer 57 ABSTRACT A manhole closure means for sealing atank manhole aperture including an elongated strongback carrying a fillcover on its underside for covering a fill aperture in the closuremeans, such strongback being hinged to the manhole closure means at oneside of the fill aperture for swinging movementover and onto the fillaperture in closed position. An elongated latch arm is hinged to themanhole closure means adjacent the fill aperture in a position oppositethe strongbackfor swinging movement toward and away from the strongback.The latch arm has its hinged end bifurcated forming an opening in whichthe free end of the strong-back is received. Positioned on the undersideof the latch arm adjacent the inner edge of the latch arm opening is atransversely disposed downwardly extending ridge. The strongback has atleast one transverse recess formed in its top side adjacent its free endfor receiving the latch arm ridge when the strongback free end isinserted in the latch arm opening, thereby firmly and securely lockingthe strongback and its fill cover over the fill aperture in closedposition thereby effecting an over-center mechanism that prevents thetill cover from opening inadvertently due to impact or shock. The fillcover may also include a springwell and an annular gasket clampedbetween a cover disc and a gasket retainer, with the cover disc beingthreaded to the springwell. The fill cover may also include an integralspringwell and a dovetail gasket carried in an undercut groove. The fillcover may also omit the springwell and secure resilient action by meansof a resilient Belleville disc included in the fill cover structure.This resilient action is adequate for latching purposes, but notadequate for venting.

12 Claims, 6 Drawing Figures I PAIENTED JUL 1 0 ms SHEEI 3 0f 4 7/1r//////// waww m 7/4 7////////////////// //VV INVENTOR. Jase/ H H DEF vCOMBINATION MANHOLE AND FILL This invention relates to tank combinationmanhole closure and fill covers and more particularly to a fill coverhaving a quick-release over-center latch mecha-.

needed and is easily unlatched by jolts, impacts or jar-' ring.

There has long been a needfor a combination tank manhole and fill coverthat not only effects a secure, tight seal, but also provides a latchingmechanism which operates on an overcenter action in which work (force xdistance) must be performed to effect unlatching, thereby providing alatch that cannot be opened inadvertently if subjected to shocks, joltsor impact.

The invention is particularly applicable to tanks containing flammableliquids. In many instances, such tanks are mounted on vehicles such ashighway tank trucks. In such instances, government regulations requireemergency venting to handle rapid, excessive pressure build-up withinthe tank such as occurs from a fireand which cannot be handled by thenormal vents. This rapid, excessive pressure build-up is more dangerousthan fire for an explosion or a rupture in the tank may result,accompanied by spreading of fire in the form of a flaming liquid.

Heretofore, a substantial part of emergency venting depended upon afusible plug or disc which melted when its temperature reached a givenamount. However, such a fusible plug has several disadvantages includingdependency upon a given elevated temperature for operation. There aresiutations wherein rapid, excessive pressure build-up within the tank,due to a fire, will not generate the required elevated temperature inproximity to or at the fusible plug because of location of the firerelative to the plug. In other situations, where the tank may havefallen on its side or be upside down, the liquid therein will cover thefusible plug and retard or prevent melting of the fusible plug.Additionally, tank manhole covers are most dangerous to open when thetank contains unexpected pressure.

Many prior fill cover latching mechanisms depend on friction or aninterlock to maintain the latch in closed position. Such structures arehazardous in that the latch may jar open if subjected to severe jolts orimpact.

Therefore, it is an object of the invention to provide a tank fill coverhaving a mannual venting feature.

A further object of the invention is to provide a tank fill coverlatching mechanism having an over-center action in which work (force xdistance) must be performed to release the latch.

A further object of the invention is to provide a tank fill cover thatis relatively safe to open when the tank contains pressure.

A further object of the invention is to provide a tank fill coverlatching mechanism that neither depends on friction nor on an interlockto function.

A further object of the invention is to provide a tank fill cover of theabove type that is simple in construction, economical to manufacture andhighly effective in operation.

A further object of the invention is to provide a fill cover latchmechanism that is safe, reliable, and will not jar open due to shock asmight occur in an accident.

Briefly, the invention relates to a combination fill and manhole closuremeans. The closure means includes a fill aperture. The closure meansalso includes an elongated planar strongback hinged atone end to themanhole closure means at one side of the fill aperture for swingingmovement in a vertical plane over the till aperture. The strongback hasa fill cover on its underside for selective sealing engagement with thefill aperture when the strongback is swung over the fill aperture to aclosed position. The closure means also includes an elongatedsubstantially planar latch arm hinged at one of its ends to the manholeclosure means at the opposite side of the fill aperture for swingingmovement in the aforementioned vertical plane toward and away from thestrongback. The latch arm has its oneend (hinged end) bifurcated formingan opening for receiving the free end of the strongback therethrough.The latch arm has an elongated ridge transversely disposed on itsunderside adjacent the inner edge of the opening. The strongback has anelongated transverse recess formed in its top side adjacent its free endfor receiving the ridge therein when the strongback free end is insertedin the latch arm opening, thereby locking the strongback and its fillcover over the fill aperture in closed sealed position when the latcharm is positioned over the strongback in closed position. The ridge maybe a hook portion, a flange, or an elongated cylindrical The strongbackhas a second elongated transvers recess formed in its top side parallelto the first recess and disposed adjacent the free end of the strongbackoutwardly of the first recess. The second recess forms a secondary latchor safety stop for receiving the latch arm ridge when the latch arm ismanually disengaged from the first recess, thus partially removing thefill cover from the fill aperture to relieve unexpected internalpressure. An inclined camming surface is interposed between the recessesto provide facile movement of the latch arm ridge from one recess to theother.

Specifically, the ridge becomes disengaged from the first recessmanually and not from pressure interiorly of the tank. The second recessshould not engage the ridge unless interior pressure is present, thuscausing the fill cover to be urged upward. The secondary latch isprovided so that the operator will notbe injured if pressure is presentin the tank at time of opening. If the secondary latch were notprovided, the fill cover could be violently opened by internal pressurewith possible harm to the operator. Large volumes of gas also wouldbecome a hazard. If there is no internal pressure present, the latch armswings clear and no engagement is encountered'with the secondary latch.

The latch arm is of elongated rectangular configuration in plan, withsuch latch arm having a handle for manual grasping on the free end.thereof.

The fill cover is formed of an annular gasket retainer of lesserdiameter than the fill aperture, an annular disc of greater diameterthan the fill aperture and spaced from and disposed above the gasketretainer, and an annular gasket of greater diameter than the fillaperture and interposed between the retainer and the disc in clampedrelation, whereby the gasket contacts the periphery of the fill apertureand the disc imparts a semiresilient sealing action to the fill coverwhen it is clamped on the fill aperture. Also included in the coverstructure is a springwell disposed centrally on the cover, with the discbeing threadedly secured to or formed integral with the springwell. Inanother form of the invention, the springwell is an integral part of thefill cover or the springwell may be omitted. The springwell has avertical bore open at the top, and the strongback has a sleeve fittingon its underside and which extends partially into the top of such bore.A coil spring is disposed in the bore and is compressed between thebottom wall of the spring-well and the sleeve fitting, thereby impartinga resilient clamp effect to the fill cover when it is locked over thefill aperture.

Thus, the invention provides a tank manhole closure and fill coverhaving venting means for venting unex pected internal pressure-when thefill cover is opened manually, such fill cover having a resilientclamping effect when locked over the tank opening, thus functioning likea giant safety valve. The secondary recess forms a safety stop toprevent further opening of the fill cover and thereby providesprotection to the operator if pressure is present in the tank.

With this construction, a safer more reliable latch mechanism isprovided that cannot be jarred loose by impact. The geometry of thelatch is such that work must be performed to open the same and it wouldfunction perfectly even though the camming surfaces where frictionless.Thus, the present latch is shock resistant, safer, maintains adjustment(less wear), is less apt to disengage and open, and provides a much morereliable and positive action. Such latch includes camming surfaces thegeometry of which provides a clamping action which compresses the gasketon the fill cover and insures a tight seal. The latch neither depends onfriction nor on an interlock to function, but rather to an overcenteraction in which work must be performed to effect unlatching.

The resiliency of the lid with or without coaction with the springwelleffects an emergency venting feature of the cover C to relieve excessivepressure interiorly of the tank due to fire exposure.

Other objects and advantages of the invention will be apparent from thefollowing description taken in conjunction with the drawings wherein:

FIG. 1 is a side elevational view, partly in section, of a tankcombination manhole and fill cover of the invention and showing, indot-dash lines, such fill cover in open position, and showing the latcharm in various perative positions;

FIG. 2 is a top plan view of the fill cover shown in FIG. 1;

FIG. 3 is a side elevational sectional view of a modification of thelatch arm of the fill cover shown in FIG.

FIG. 4 is a view similar to FIG. 3, but showing a modification thereof;

FIG. 5 illustrates a modification of the device shown in FIG. 1; and

FIG. 6 illustrates a further modification of the device shown in FIG. 1.

Although the invention is shown and described herein with reference totransportation tanks, it will be understood that it may be applied toany type of fluid holding container.

The terms and expressions which have been employed are used as terms ofdescription, and not of limitation, and there is no intention, in theuse of such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

Referring first to FIGS. 1 and 2, there is shown a tank combinationmanhole and fill cover closure means of the invention, generallydesignated as A, and disposed on a liquid storage tank T. The tank Tcontains in its upper portion, a manhole opening defined by an endless,annular, peripheral ring or collar 10 projecting upwardly from the tank.Secured to the upper end of the collar 10 by means of the clamping ring11 (FIG. 2), clips 12, and bolt 13 is an annular manhole closure 14,having an inner, peripheral, annular curb 15 forming a seat for theclosure means A, such annular curb 15 also defining a fill aperture 16.

Disposed on one side of the aperture 16 are hinge lugs 20. Hinged to thelugs 20 by means of the pin 21 is an elongated, planar, lock arm orstrongback 22. The strongback 22 carries on its underside a fill cover,generally designated as C, which will later be described in detail.Formed in the outer end portion of the strongback 22 is a first recess24, which merges outwardly into a camming surface or projection 25, suchsurface ending with a second recess or secondary latch 26. The surface25 includes an inclined camming surface 25a extending to the recess 26,and an inclined camming surface 25b extending to the recess 24.

Secured centrally to the strongback 22 is an attach fitting 28 having acentral vertical bore 30 in which is disposed a bolt 32. The lower endof the bolt 32 passes through a bore 34 in springwell 36 such thattightening of the lock nut 38 on the bolt 32 draws the springwellupwardly toward the fitting 28, such fitting being telescoped into thespringwell bore 40. A compressed coiled spring 42 is disposed in thebore 40 and is compressed between the fitting 28 and the floor of thespringwell 36. The cover C is threaded onto the spring well 36 as shown.

The fill cover C includes a gasket 50 which is sandwiched or clampedbetween a metal gasket retainer 52 and a metal disc 54 which is threadedonto the springwell 36, whereby the retainer 52 is clamped against thespringwell flange 56. With this construction, there is effected aresilient action to the fill cover C such that excessive build-up ofpressure due to fire exposure within the tank T will act against thefill cover C, and in turn the spring 42 to cause the fill cover to riseand vent such pressure.

A vent 60 is secured to the fill cover C, such vent, per se, forming nopart of the present invention and is described in detail in U.S. Pat.No. 3,302,658.

Disposed adjacent the fill aperture 16 opposite the lugs 20, are hingelugs 64. Hinged to the lugs 64 by means of a hinge pin 66 is anelongated rectangular latch arm 68 having a handle 69 on its free end.The

hinged end of the latch arm 68 is bifurcated to providean opening 70 forreceiving the free end of the strongback 22 therethrough. The latch arm68 has an eloncess 2d, thence cam over the camming surfaces 25b, 25 and25a, and lock into the secondary latch or recess 26, thereby preventingthe fill cover from opening further and also providing a controlled orlimited vent for release of pressurized fluids. The fill cover may befully opened only when pressure in the tank is exhausted.

It is to be particularly emphasized that the latch includes the cammingsurfaces 25a and 25b the geometry of which provides an over-centeraction effecting a clamping action which compressed the gasket 50 andinsures a tight seal. Such latching device neither depends on frictionnor an interlock to function, but rather to an over-center action inwhich work must be performed by the operator before unlatching can beeffected and it would function perfectly even though the cammingsurfaces 25a, 25b were frictionless. Thus, the present latch mechanismis more reliable, safer, and much less apt to open due to shockresulting from an accident.

As aforementioned, the secondary latch is provided so that the operatorwill not be injured if internal pressure is present in the tank at timeof opening. If this secondary latch were not provided, the fill cover Cwould be violently opened to the full opened position with possible harmto the operator. Also, large volumes of gas would become a hazard. Ifthere is no internal pressure present, latch arm 68 swings clear and noengagement with secondary latch 26 is encountered.

Prior art latches depended heavily on friction to maintain engagement.This is not the case with the present latch as it would function eventhough surfaces were frictionless. In other words, to disengage thepresent latch work has to be performed (force x distance). The rotatingof latch arm 68 from the closed position actually causes a downwardmotion of strongback 22 against an upward force created by spring 42.

gated transverse recess 24 formed in its top side adjacent its free endfor receiving the ridge 72 therein when the strongback free end isinserted in the latch arm opening 70, thereby locking the strongback andits fill cover C over the fill aperture 16 in closed sealed positionwhen the latch arm 68 is positioned over the strongback in closedposition.

In one form of the invention, the strongback 22 has a second elongatedtransverse recess 26 formed in its top side parallel to the first recess24 and disposed adjacent the free end of the strongback 22 outwardly ofthe first recess 24. The second recess 26 forms a secondary latch orsafety stop for receiving the latch arm ridge 72 when such ridge isdisengaged from the first recess24, when internal pressure is present;The camming surfaces 25a, 25 and 25b are interposed between the recesses24, 26 to provide facile movement of the latch arm ridge 72 from onerecess to the other.

Also included are the pair of strongback hinge lugs 20 secured to themanhole closure '14 at the one side of the fill aperture 16. The hingedend of the strongback is bifurcated, with such bifurcated end beinghinged to such strongback hinge lugs 20. In like manner, a pair of latcharm hinge lugs 64 are secured to the manhole closure plate 14 at theopposite side of the till aperture 16, with the bifurcated end of thelatch arm 68 being hinged to the latch arm hinge lugs 64.

The latch arm 68 is of elongated rectangular configuration in plan, andhas the handle 69 for manual graspr ing of the free end thereof.

Thus work must be performed and the camming surfaces must go over centerbefore the unlatching operation is complete.

In FIGS. 1 and 2 the ridge 72 is formed by a downwardly extendingelongated transversely disposed hook portion formed in the latch arm 68adjacent the inner edge of the latch opening 70.

FIG. 3 illustrates a modified latch arm 68a having a ridge in the formof an elongated cylindrical pin 80.

FIG. 4 illustrates a modified latch arm 68b having a ridge in the formof downwardly extendingtranversely disposed flange 82.

Thus, the invention provides a tank manhole closure means A forselectively sealing a fill aperture 16 in a liquid containing tank Tincluding an elongated planar strongback 22 hinged at one end to thetank T at one side of the fill aperture 16 for swinging movement in avertical plane over and onto the fill aperture The strongback has a fillcover C on its underside for selective sealing engagement with the fillaperture 16 when the strongback is swung over the fill aperture to aclosed position. An elongated substantially planar latch arm 68 ishinged at one of its ends to the manhole closure 14 at the opposite sideof the fill aperture 16 for swinging movement in such vertical planetoward and away from the strongback 22. The latch arm has its one endbifurcated forming an opening 70 for receiving the free end of thestrongback 22 therethrough. The latch arm 68has an elongated dependingridge 72 trans versely disposed on its underside adjacent the inner edgeof the opening 70. The strongback 22 has an elon- The fill cover Cincludes the annular gasket retainer 52 of less diameter than the fillaperture 16, an annular disc 54 of greater diameter than the fillaperture 16 and spaced from and disposed above the gasket retainer 52,and an annular gasket 50 of greater diameter than the fill aperture 116and interposed between the retainer 52 and the disc 54 in clampedrelation, whereby the gasket 50 contacts the seat or periphery 15 of thefill aperture 16 and the disc 54 imparts a semi-resilient sealing actionto the fill cover C when it is clamped on the fill aperture 16.

Such resiliency of the fill cover C, along with the springwell, effectsan emergency venting feature actuated solely by pressure within thetank. Specifically, if pressure builds up excessively interiorly of thetank, the

fill cover C will lift off the seat 15 to relieve such pressure.

Further included is the springwell 36 disposed centrally on the fillcover C, the disc 54 being threadedly secured to the springwell. Thespringwell 36 has a vertical bore 40 open at the top. The strongback 22has a sleeve fitting 28 on its underside which extends partially intothe top of the bore 40. A coil spring 42 is disposed in the bore 40 andis compressed between the bottom wall of the springwell and the sleevefitting 28, thereby also imparting a resilient clamping effect to thefill cover C when it is locked over the aperture 16.

In FIG. 1, the latch of the invention is shown in combination with afill cover C having a centrally disposed springwell 36, such coverincluding the gasket retainer 52, the disc 54, and the gasket 50 clampedtherebetween as aforementioned.

In FIG. 5, the latch of the invention is shown in combination with afill cover C-l (similar in construction to cover C) without aspringwell., but with a vent valve In FIG. 6, the latch of the inventionis shown in combination with a fill cover C-2 of single plateconstruction andhaving a dovetail gasket 90 attached to the peripherythereof. The cover C-2 has a springwell 36a secured centrally theretoand a vent 60b disposed between the springwell and the periphery of thefill cover.

Thus, the fill cover C may or may not include a spring-well. If thespringwell is included it may be threaded on the fill cover as shown inFIG. 1, or formed integral with the fill cover as shown in FIG. 6.

The fill cover may omit the springwell and effect resilient action ofthe cover by means of a resilient Belleville disc 84 as shown in FIG. 5.Such resilient action is adequate for latching purposes, but not forventing.

What is claimed is:

1. A tank manhole closure means for selectively sealing a fill aperturetherein comprising, an elongated planar strongback hinged at one end tothe manhole closure means at one side of the aperture for swingingmovement in a vertical plane over the aperture, said strongback having afill cover on its underside for selective sealing engagement with theaperture when the strongback is swung over the aperture to a closedposition, and an elongated substantially planar latch arm hinged at oneof its ends to the tank at the opposite side of the aperture forswinging movement in said vertical plane toward and away. from thestrongback, said latch arm having its one end bifurcated forming anopening for receiving the free end of the strongback therethrough, saidlatch arm having an elongated depending ridge transversely disposed onits underside adjacent the inner edge of the opening, said strongbackhaving an elongated transverse recess formed in its top side adjacentits free end and extending below the surface of such top side forreceiving said ridge therein when the strongback free end is inserted inthe latch arm opening thereby locking the strongback and its cover overthe fill aperture in closed sealed position when the latch arm ispositioned over the strongback in closed position, the entrance surfaceof said recess being an inclined convex curved camming surface on whichthe ridge slides and is thus cammed into the recess, said latch armridge comprising a downwardly extending elongated transversely disposedhook portion formed in' the latch arm adjacent the inner edge of thelatch arm opening.

2. The structure of claim 1 wherein said strongback has a secondelongated transverse recess formed in its top side parallel to thefirst-named recess and disposed adjacent the free end of the strongbackoutwardly of the first-named recess, said second recess forming a safetystop for receiving said latch arm ridge if such ridge becomes disengagedfrom the first-named recess.

3. The'structure of claim 2 wherein a projection having camming surfaceson both sides thereof is interposed between the recesses to providefacile clamping movement of the latch arm ridge from one recess to theother, thereby effecting an over-center action to compress the cover andinsure a tight seal in said closed position.

4. The structure of claim 1 and further including a pair of strongbackhinge lugs secured to the manhole closure at said one side of theaperture, the hinged end of said strongback being bifurcated with suchbifur cated end being hinged to said strongback hinge lugs.

5. The structure of claim 1 and further including a pair of latch armhinge lugs secured to the manhole closure at said opposite side of theaperture with the bifurcated end of the latch arm being hinged to saidlatch arm hinge lugs.

6. The structure of claim 1 wherein said latch arm is of elongatedrectangular configuration in plan, said latch arm having a handle formanual grasping on the free end thereof.

7. The structure of claim 1 wherein said cover includes an annulargasket retainer of lesser diameter than the aperture, an'annular disc ofgreater diameter than the aperture and spaced from and disposed abovethe gasket retainer, and an annular gasket of greater diameter than theaperture and interposed between the retainer and the disc in clampedrelation, whereby the gasket contacts the periphery of the aperture andthe disc imparts a semi-resilient sealing action to the cover when it isclamped on the aperture.

8. The structure of claim 7 and further including a springwell disposedcentrally on the cover, said disc being threadedly secured to thespringwell, said springwell having a vertical bore open at the top, saidstrongback having a sleeve fitting on its underside and extendingpartially into the top of the bore, and a coil spring disposed in thebore and compressed between the bottom wall of the springwell and saidsleeve fitting, thereby imparting a resilient clamping effect on thecover when it is locked over the aperture.

9. The structure of claim 7 and further including a vent valve disposedcentrally thereon.

10. The structure of claim 1 wherein the cover is of single plateconstruction, said cover having a dovetail gasket attached to theperiphery thereof.

11. A tank manhole closure means for selectively sealing a fill aperturetherein comprising, an elongated planar strongback hinged at one end tothe manhole closure means at one side of the aperture for swingingmovement in a vertical plane over the aperture, said strongback having afill cover on its underside for selective sealing engagement with theaperture when the strongback is swung over the aperture to a closedposition, and an elongated substantially planar latch arm hinged at oneof its ends to the tank at the opposite side of the aperture forswinging movement in said vertical plane toward and away from thestrongback, said latch arm having its one end bifurcated forming anopening for receiving the free end of the strongback therethrough, saidlatch arm having an elongated depending ridge transversely disposed onits underside adjacent the inner edge of the opening, said strongbackhaving an elongated transverse recess formed in its top side adjacentits free end and extending below the surface of such top side forreceiving said ridge therein when the strongback free end is inserted inthe latch arm opening thereby locking the strongback and its cover overthe fill aperture in closed sealed position when the'latch arm ispositioned over the strongback in closed position, the entrance surfaceof said recess being an inclined convex curved camming surface on whichthe ridge slides and is thus cammed into the recess, said latch armridge comprising a downwardly extending transversely disposed flangeformed in the latch arm adjacent the inner edge of the latch armopening.

12. A tank manhole closure means for selectively sealing a fill aperturetherein comprising, an elongated planar strongback hinged at one end tothe closure means at one side of the aperture for swinging movement in avertical plane over the aperture, said strong- 9 I back carrying a coveron its underside for selective sealing engagement with the aperture whenthe strongback is swung over the aperture to a closed position, anelongated planar latch arm hinged at one of its ends to the closuremeans at the opposite side of the aperture for swinging movement in saidvertical plane toward and away from the strongback, said latch armhavingits one end bifurcated forming an opening for receiving the free end ofthe strongback therethrough, said latch arm having an elongated ridgetransversely disposed on its underside adjacent the inner edge of theopening, said strongback having an elongated transverse recess formed inits top side adjacent its free end for receiving said ridge therein whenthe strongback free end is inserted in the latch arm opening therebylocking the strongback and its cover over the aperture in closed sealedposition when the latch is positioned over the strongback in closedposition, said latch arm ridge including a downwardly extendingelongated transversely disposed hook portion formed in the latch armadjacent wardly of the first-named recess, said second recess I forminga safety stop for receiving said latch arm ridge if such ridge becomesdisengaged from the first-named recess, there being a camming surfaceinterposed between the recesses to provide facile movement of the latcharm ridge from one recess to the other, a pair of strongback hinge lugssecured to the closure means at said one side of the aperture, thehinged end of said strongback being bifurcated with such strongbackbifurcated end being hinged to said strongback hinge lugs, and a pair oflatch arm hinge lugs secured to the closure means at said opposite sideof the aperture with the bifurcated end of the latch arm. being hingedto said latch arm hinge lugs, said latch arm being of elongatedrectangular configuration in plan, said latch arm having a handle formanual grasping on the free end thereof. i

1. A tank manhole closure means for selectively sealing a fill aperturetherein comprising, an elongated planar strongback hinged at one end tothe manhole closure means at one side of the aperture for swingiNgmovement in a vertical plane over the aperture, said strongback having afill cover on its underside for selective sealing engagement with theaperture when the strongback is swung over the aperture to a closedposition, and an elongated substantially planar latch arm hinged at oneof its ends to the tank at the opposite side of the aperture forswinging movement in said vertical plane toward and away from thestrongback, said latch arm having its one end bifurcated forming anopening for receiving the free end of the strongback therethrough, saidlatch arm having an elongated depending ridge transversely disposed onits underside adjacent the inner edge of the opening, said strongbackhaving an elongated transverse recess formed in its top side adjacentits free end and extending below the surface of such top side forreceiving said ridge therein when the strongback free end is inserted inthe latch arm opening thereby locking the strongback and its cover overthe fill aperture in closed sealed position when the latch arm ispositioned over the strongback in closed position, the entrance surfaceof said recess being an inclined convex curved camming surface on whichthe ridge slides and is thus cammed into the recess, said latch armridge comprising a downwardly extending elongated transversely disposedhook portion formed in the latch arm adjacent the inner edge of thelatch arm opening.
 2. The structure of claim 1 wherein said strongbackhas a second elongated transverse recess formed in its top side parallelto the first-named recess and disposed adjacent the free end of thestrongback outwardly of the first-named recess, said second recessforming a safety stop for receiving said latch arm ridge if such ridgebecomes disengaged from the first-named recess.
 3. The structure ofclaim 2 wherein a projection having camming surfaces on both sidesthereof is interposed between the recesses to provide facile clampingmovement of the latch arm ridge from one recess to the other, therebyeffecting an over-center action to compress the cover and insure a tightseal in said closed position.
 4. The structure of claim 1 and furtherincluding a pair of strongback hinge lugs secured to the manhole closureat said one side of the aperture, the hinged end of said strongbackbeing bifurcated with such bifurcated end being hinged to saidstrongback hinge lugs.
 5. The structure of claim 1 and further includinga pair of latch arm hinge lugs secured to the manhole closure at saidopposite side of the aperture with the bifurcated end of the latch armbeing hinged to said latch arm hinge lugs.
 6. The structure of claim 1wherein said latch arm is of elongated rectangular configuration inplan, said latch arm having a handle for manual grasping on the free endthereof.
 7. The structure of claim 1 wherein said cover includes anannular gasket retainer of lesser diameter than the aperture, an annulardisc of greater diameter than the aperture and spaced from and disposedabove the gasket retainer, and an annular gasket of greater diameterthan the aperture and interposed between the retainer and the disc inclamped relation, whereby the gasket contacts the periphery of theaperture and the disc imparts a semi-resilient sealing action to thecover when it is clamped on the aperture.
 8. The structure of claim 7and further including a springwell disposed centrally on the cover, saiddisc being threadedly secured to the springwell, said springwell havinga vertical bore open at the top, said strongback having a sleeve fittingon its underside and extending partially into the top of the bore, and acoil spring disposed in the bore and compressed between the bottom wallof the springwell and said sleeve fitting, thereby imparting a resilientclamping effect on the cover when it is locked over the aperture.
 9. Thestructure of claim 7 and further including a vent valve disposedcentrally thereon.
 10. The structure of claim 1 wherein the cover is ofsingle plate constructiOn, said cover having a dovetail gasket attachedto the periphery thereof.
 11. A tank manhole closure means forselectively sealing a fill aperture therein comprising, an elongatedplanar strongback hinged at one end to the manhole closure means at oneside of the aperture for swinging movement in a vertical plane over theaperture, said strongback having a fill cover on its underside forselective sealing engagement with the aperture when the strongback isswung over the aperture to a closed position, and an elongatedsubstantially planar latch arm hinged at one of its ends to the tank atthe opposite side of the aperture for swinging movement in said verticalplane toward and away from the strongback, said latch arm having its oneend bifurcated forming an opening for receiving the free end of thestrongback therethrough, said latch arm having an elongated dependingridge transversely disposed on its underside adjacent the inner edge ofthe opening, said strongback having an elongated transverse recessformed in its top side adjacent its free end and extending below thesurface of such top side for receiving said ridge therein when thestrongback free end is inserted in the latch arm opening thereby lockingthe strongback and its cover over the fill aperture in closed sealedposition when the latch arm is positioned over the strongback in closedposition, the entrance surface of said recess being an inclined convexcurved camming surface on which the ridge slides and is thus cammed intothe recess, said latch arm ridge comprising a downwardly extendingtransversely disposed flange formed in the latch arm adjacent the inneredge of the latch arm opening.
 12. A tank manhole closure means forselectively sealing a fill aperture therein comprising, an elongatedplanar strongback hinged at one end to the closure means at one side ofthe aperture for swinging movement in a vertical plane over theaperture, said strongback carrying a cover on its underside forselective sealing engagement with the aperture when the strongback isswung over the aperture to a closed position, an elongated planar latcharm hinged at one of its ends to the closure means at the opposite sideof the aperture for swinging movement in said vertical plane toward andaway from the strongback, said latch arm having its one end bifurcatedforming an opening for receiving the free end of the strongbacktherethrough, said latch arm having an elongated ridge transverselydisposed on its underside adjacent the inner edge of the opening, saidstrongback having an elongated transverse recess formed in its top sideadjacent its free end for receiving said ridge therein when thestrongback free end is inserted in the latch arm opening thereby lockingthe strongback and its cover over the aperture in closed sealed positionwhen the latch is positioned over the strongback in closed position,said latch arm ridge including a downwardly extending elongatedtransversely disposed hook portion formed in the latch arm adjacent theinner edge of the latch arm opening, said strongback having a secondelongated transverse recess and disposed adjacent the free end of thestrongback outwardly of the first-named recess, said second recessforming a safety stop for receiving said latch arm ridge if such ridgebecomes disengaged from the first-named recess, there being a cammingsurface interposed between the recesses to provide facile movement ofthe latch arm ridge from one recess to the other, a pair of strongbackhinge lugs secured to the closure means at said one side of theaperture, the hinged end of said strongback being bifurcated with suchstrongback bifurcated end being hinged to said strongback hinge lugs,and a pair of latch arm hinge lugs secured to the closure means at saidopposite side of the aperture with the bifurcated end of the latch armbeing hinged to said latch arm hinge lugs, said latch arm being ofelongated rectangular configuration in plan, said latch arm having ahandle for manual grasping on the free end thereOf.